Hillsborough County investigators started piecing together what happened on the still-dark morning of Sept. 21. In a 206-page report released Wednesday, they say they now know: Deputy Mark Longway ran a red light.

Their determination is based on the witnesses, video evidence and timing of traffic lights.

No one will ever know why Longway didn't stop, but investigators know he wasn't distracted by a cell phone, computer or radio — none of those devices were in use at the time.

"We're just thankful now that we can bring closure to the Longway family and to the truck driver and his family," said Deputy Larry McKinnon, a sheriff's spokesman. "A lot of loved ones on both sides were waiting for this."

After 5 a.m., Longway, 48, drove north on Florida Avenue at 36 mph. After a night shift, he was headed home.

Lamont Ashley, 39, had also been working all night. He was trying to make his last delivery when he got off Interstate 275 by mistake. He drove along Scott Street at 27 mph to get back on.

A woman also on her way home from work saw a traffic light turn red and a cruiser continue past it. Is he going to stop? Maria Wallace asked herself.

The deputy must have seen the truck. From the center lane, he swerved hard to the left and stepped on the brakes. The crash sounded like an explosion.

The semi driver felt something hit his truck, he told investigators. He checked his outside mirror and saw the car under his trailer. He stopped as fast as he could, got out, and called 911.

"A cruiser ran into the tractor trailer," he said. "Scott Street and Florida Avenue. He came through. I had a green light. I was going through and he just came through the red light. …

"I need an ambulance!"

But the deputy suffered head trauma. He died on the scene.

The truck driver did not return messages left by the Times.

Detectives found a pedestrian who had been waiting to cross Scott Street when he heard the boom. William Cunningham told investigators the signal said not to cross, indicating drivers on Scott Street had the right of way.

Video on a nearby county bus shows its driver jerking her head toward the crash at 5:16:08 a.m. That told investigators exactly when the crash happened.

Surveillance video on the Florida Avenue Chem-Tel building showed the truck stopped at a light on Tampa Street, then continuing toward Florida Avenue.

A city traffic engineer was able to determine, based on the truck's path and the time he was provided, that the truck would have had the right of way.

Longway, an Air Force veteran and distinguished deputy, left behind a wife, two adult daughters and a grandchild.

He was wearing his seat belt.

Times staff writers Shelley Rossetter and Dan Sullivan and researcher Shirl Kennedy contributed to this report.